U.S. patent application number 13/611437 was filed with the patent office on 2013-01-03 for mobile station-assisted interference mitigation.
This patent application is currently assigned to RESEARCH IN MOTION LIMITED. Invention is credited to William Anthony Gage, Robert Novak.
Application Number | 20130003589 13/611437 |
Document ID | / |
Family ID | 47138588 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130003589 |
Kind Code |
A1 |
Gage; William Anthony ; et
al. |
January 3, 2013 |
MOBILE STATION-ASSISTED INTERFERENCE MITIGATION
Abstract
Devices and methods are provided for using a mobile station to
mitigate interference between wireless access points. A mobile
station communicates interference mitigation data corresponding to
a first and second set of radio resources between a first and
second wireless access point (AP). The interference mitigation data
is processed by the first wireless AP to resolve conflicts in the
claiming, and subsequent assignment, of the first and second radio
resource assignments to the mobile station.
Inventors: |
Gage; William Anthony;
(Stittsville, CA) ; Novak; Robert; (Stittsville,
CA) |
Assignee: |
RESEARCH IN MOTION LIMITED
Waterloo
CA
|
Family ID: |
47138588 |
Appl. No.: |
13/611437 |
Filed: |
September 12, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CA2011/050286 |
May 10, 2011 |
|
|
|
13611437 |
|
|
|
|
Current U.S.
Class: |
370/252 ;
370/329 |
Current CPC
Class: |
H04W 72/04 20130101;
H04L 5/0073 20130101; H04W 72/00 20130101; H04J 11/0023 20130101;
H04J 11/005 20130101 |
Class at
Publication: |
370/252 ;
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04; H04W 24/00 20090101 H04W024/00 |
Claims
1. A mobile station comprising: processing logic operable to
mitigate interference between a first wireless access point (AP) of
a plurality of access points (APs) and at least a second wireless
AP of the plurality of APs; processing logic operable to determine
a first set of radio resources claimed for assignment by the first
AP; processing logic operable to determine a second set of radio
resources claimed for assignment by the second AP; and processing
logic operable to communicate interference mitigation data
associated with the first and second sets of radio resources to the
first wireless AP such that interference is mitigated.
2. The mobile station of claim 1, wherein the mobile station is
operable to communicate interference mitigation data comprising the
second set of radio resources to the first wireless AP.
3. The mobile station of claim 1, wherein: at least one of the
radio resources from the first set of radio resources claimed by
the first wireless AP is also included in the second set of radio
resources claimed contemporaneously by the second wireless AP; and
the mobile station is operable to communicate interference
mitigation data comprising the second set of radio resources to the
first wireless AP.
4. The mobile station of claim 1, wherein: at least one of the
radio resources from the first set of radio resources claimed by
the first wireless AP is also included in the second set of radio
resources claimed contemporaneously by the second wireless AP; and
the mobile station is operable to communicate interference
mitigation data comprising radio resource assignment conflict data
to the first wireless AP, the radio resource assignment conflict
data comprising the set of conflicted resources included in both
the first and second sets of radio resources.
5. The mobile station of claim 1, wherein the mobile station is
operable to process the first and second sets of claimed radio
resources to generate interference mitigation data comprising radio
resource selection data, the radio resource selection data
comprising a set of selected radio resources from the first set of
radio resources and a preference value assigned by the mobile
station to each resource in the set of selected radio
resources.
6. The mobile station of claim 1, comprising: processing logic
operable to determine a first set of resources claimed for
assignment by a wireless AP for use in a first transmit power zone
(TPZ) corresponding to a first transmit power level (TPL);
processing logic operable to determine a second set of resources
claimed for assignment by the wireless AP for use in a second TPZ
corresponding to a second TPL; wherein the mobile station is
operable to respectively determine claims for the first and second
set of resources when the mobile station is located within the
first and second TPZs.
7. The mobile station of claim 6, comprising: processing logic
operable to determine that the claim for the first set of resources
is transmitted by the wireless AP at the first TPL; processing
logic operable to determine that the claim for the second set of
resources is transmitted by the wireless AP at the second TPL; and
processing logic operable to determine that the mobile station is
located within the first TPZ if the mobile station successfully
decodes the claim for the first set of resources and is located
within the second TPZ if the mobile station successfully decodes
the claim for the second set of resources.
8. The mobile station of claim 6, comprising: processing logic
operable to determine that a first set of power reference signals
(PRS) transmitted by the wireless AP at the first transmit power
level (TPL) is associated with the first transmit power zone (TPZ);
processing logic operable to determine that a second set of PRS
transmitted by the wireless AP at the second TPL is associated with
the second TPZ; and processing logic operable to determine that the
mobile station is located within the first TPZ if the mobile
station successfully decodes the first set of PRS and is located
within the second TPZ if the mobile station successfully decodes
the second set of PRS.
9. The mobile station of claim 6, comprising: processing logic
operable to determine that a first set of pathloss data is
associated with the first transmit power zone (TPZ); processing
logic operable to determine that a second set of pathloss data is
associated with the second TPZ; processing logic operable to
determine a transmit power level (TPL) associated with a set of
power reference signals (PRS) transmitted by the wireless AP;
processing logic operable to successfully decode the set of PRS,
measure a Signal to Interference-plus-Noise Ratio (SINR) of the
received PRS, and calculate a pathloss of the PRS; and processing
logic operable to determine that the mobile station is located
within the first TPZ if the calculated pathloss matches the first
set of pathloss data and is located within the second TPZ if the
calculated pathloss matches the second set of pathloss data.
10. A method for mitigating interference between wireless access
points, comprising: mitigating interference between a first
wireless access point (AP) of a plurality of access points (APs)
and at least a second wireless AP of the plurality of APs by using
processing logic of a mobile station; determining, by the mobile
station, a first set of radio resources claimed for assignment by
the first AP; determining, by the mobile station, a second set of
radio resources claimed for assignment by the second AP;
communicating, by the mobile station, interference mitigation data
associated with the first and second sets of radio resources to the
first wireless AP such that interference is mitigated.
11. The method of claim 10, wherein the mobile station communicates
interference mitigation data comprising the second set of radio
resources to the first wireless AP.
12. The method of claim 10, wherein: at least one of the radio
resources from the first set of radio resources claimed by the
first wireless AP is also included in the second set of radio
resources claimed contemporaneously by the second wireless AP; and
the mobile station communicates interference mitigation data
comprising the second set of radio resources to the first wireless
AP.
13. The method of claim 10, wherein: at least one of the radio
resources from the first set of radio resources claimed by the
first wireless AP is also included in the second set of radio
resources claimed contemporaneously by the second wireless AP; and
the mobile station communicates interference mitigation data
comprising radio resource assignment conflict data to the first
wireless AP, the radio resource assignment conflict data comprising
a set of conflicted resources included in both the first and second
sets of radio resources.
14. The method of claim 10, wherein: the mobile station processes
the first and second sets of claimed radio resources to generate
interference mitigation data comprising radio resource selection
data, the radio resource selection data comprising a set of
selected radio resources from the first set of radio resources and
a preference value assigned by the mobile station to each resource
in the set of selected radio resources.
15. The method of claim 10, comprising: determining a first set of
resources claimed for assignment by a wireless AP for use in a
first transmit power zone (TPZ) corresponding to a first transmit
power level (TPL); determining a second set of resources claimed
for assignment by the wireless AP for use in a second TPZ
corresponding to a second TPL; wherein the mobile station is
operable to respectively determine claims for the first and second
set of resources when the mobile station is located within the
first and second TPZs.
16. The method of claim 15, comprising: determining that the claim
for the first set of resources is transmitted by the wireless AP at
the first TPL; determining that the claim for the second set of
resources is transmitted by the wireless AP at the second TPL; and
determining that the mobile station is located within the first TPZ
if the mobile station successfully decodes the claim for the first
set of resources and is located within the second TPZ if the mobile
station successfully decodes the claim for the second set of
resources.
17. The method of claim 15, comprising: determining that a first
set of power reference signals (PRS) transmitted by the wireless AP
at the first transmit power level (TPL) is associated with the
first transmit power zone (TPZ); determining that a second set of
PRS transmitted by the wireless AP at the second TPL is associated
with the second TPZ; and determining that the mobile station is
located within the first TPZ if the mobile station successfully
decodes the first set of PRS and is located within the second TPZ
if the mobile station successfully decodes the second set of
PRS.
18. The method of claim 15, comprising: determining that a first
set of pathloss data is associated with the first transmit power
zone (TPZ); determining that a second set of pathloss data is
associated with the second TPZ; determining the transmit power
level (TPL) associated with a set of power reference signals (PRS)
transmitted by the wireless AP; successfully decoding the set of
PRS, measuring a Signal to Interference-plus-Noise Ratio (SINR) of
the received PRS, and calculating a pathloss of the PRS; and
determining that the mobile station is located within the first TPZ
if the calculated pathloss matches the first set of pathloss data
and is located within the second TPZ if the calculated pathloss
matches the second set of pathloss data.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of International Patent Application
No. PCT/CA2011/050286, entitled MOBILE STATION-ASSISTED
INTERFERENCE MITIGATION, by inventors William Gage and Robert
Novak, Attorney Docket No. 39424-1-WO-PCT, filed on May 10, 2011,
now pending, and incorporated by reference in its entirety.
[0002] International Patent Application No. PCT/CA2011/050285,
entitled SYSTEM AND METHOD FOR MOBILE STATION-ASSISTED INTERFERENCE
MITIGATION, by inventors William Gage and Robert Novak, Attorney
Docket No. 39424-WO-PCT, filed on May 10, 2011, describes exemplary
methods and systems and is incorporated by reference in its
entirety.
[0003] International Patent Application No. PCT/CA2011/050287,
entitled ACCESS POINT FOR MOBILE STATION-ASSISTED INTERFERENCE
MITIGATION, by inventors William Gage and Robert Novak, Attorney
Docket No. 39424-2-WO-PCT, filed on May 10, 2011, describes
exemplary methods and systems and is incorporated by reference in
its entirety.
BACKGROUND
[0004] The realization of greater capacity in today's wireless
communications environments may require the achievement of a
consistently higher signal to interference-plus-noise ratio (SINR)
over a significant percentage of a cell's coverage area. Yet
achievement of such a goal will require, in general, smaller cells
or alternatively, operation in a smaller region of a cell when
operating at a given transmit power level. Hence, the current
network model of higher-power outdoor macro cells will need to be
augmented by lower-power indoor and outdoor micro- and pico-cells.
While such a move towards smaller cells will significantly increase
the number of access points within a cellular system, it will also
lead to significant coverage overlap, both planned and unplanned,
between cells.
[0005] Co-ordination of transmission and reception in today's
cellular systems has been designed with the philosophy of "smart
network, dumb user equipment," reflecting the telephone-centric
mindset of a previous era. The "smart" network model is based on
the premise that the network has a global view, and overall
control, of everything that is occurring within the network.
However, this assumption breaks down in a heterogeneous coverage
environment as it is likely that no single, centralized network
entity will have a global view and overall control. As an example,
transmission and reception within a given cell is coordinated by
the Access Point (AP) responsible for that cell. However, operation
across cell boundaries may be un-coordinated due to different
administrative domains or to difficulties encountered when
communicating between APs. As a consequence, completely
un-coordinated operation may ultimately result in unacceptable
levels of interference that could negate the benefits of improved
signal levels garnered through the use of smaller cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present disclosure may be understood, and its numerous
objects, features and advantages obtained, when the following
detailed description is considered in conjunction with the
following drawings, in which:
[0007] FIG. 1 depicts an exemplary system node in which the present
disclosure may be implemented;
[0008] FIG. 2 shows a wireless-enabled communications environment
including an embodiment of a mobile station;
[0009] FIG. 3 is a simplified block diagram of a heterogeneous
wireless network environment comprising a plurality of macro cells,
micro cells, and pico cells;
[0010] FIG. 4 is a simplified block diagram showing the detrimental
effect of co-channel inter-cell interference as mitigated in a
single frequency network;
[0011] FIG. 5 shows a process signal flow for mobile
station-assisted radio resource conflict resolution;
[0012] FIG. 6 shows a process signal flow for mobile
station-assisted radio resource assignment;
[0013] FIGS. 7a-b are a simplified block diagram of
power-controlled conflict resolution to mitigate interference
between wireless access points;
[0014] FIG. 8 shows a process signal flow for power-controlled
conflict resolution to mitigate interference between wireless
access points;
[0015] FIG. 9 is a simplified block diagram of a mobile
station-assisted inter-access point (AP) communications
environment;
[0016] FIG. 10 simplified topological diagram showing downlink
transmit power zones;
[0017] FIG. 11 is a simplified topological diagram showing
inter-cell interference zones;
[0018] FIG. 12 is a simplified topological diagram showing mobile
station serving and contending cell sets;
[0019] FIG. 13 shows a process signal flow for interference
mitigation procedures;
[0020] FIG. 14 is a simplified block diagram of a resource claims
and contention resolution process;
[0021] FIG. 15 is a simplified block diagram of a compact claimed
resource map;
[0022] FIG. 16 is a simplified topological diagram showing the
effect of an interfering mobile station transmitting on the uplink
from inside of an inter-cell interference zone (ICIZ);
[0023] FIG. 17 is a is a simplified topological diagram showing the
implementation of a mobile station to calculate path loss prior to
transmitting on the uplink from inside of an ICIZ;
[0024] FIG. 18 is a is a simplified topological diagram showing a
contention-based system as implemented for mitigating interference
in a wireless local area network (WLAN).
DETAILED DESCRIPTION
[0025] The present disclosure is directed in general to wireless
communications systems and methods for operating same. In one
aspect, the present disclosure relates to devices and methods for
using a mobile station to mitigate interference between access
points in a heterogeneous wireless network environment.
[0026] An embodiment is directed to a mobile station comprising
processing logic operable to mitigate interference between a first
wireless access point (AP) of a plurality of access points (APs)
and at least a second wireless AP of the plurality of APs,
processing logic operable to determine a first set of radio
resources claimed for assignment by the first AP, processing logic
operable to determine a second set of radio resources claimed for
assignment by the second AP, and processing logic operable to
communicate interference mitigation data associated with the first
and second sets of radio resources to the first wireless AP such
that interference is mitigated.
[0027] An embodiment is directed to a method for mitigating
interference between wireless access points, comprising mitigating
interference between a first wireless access point (AP) of a
plurality of access points (APs) and at least a second wireless AP
of the plurality of APs by using processing logic of a mobile
station, determining, by the mobile station, a first set of radio
resources claimed for assignment by the first AP, determining, by
the mobile station, a second set of radio resources claimed for
assignment by the second AP, communicating, by the mobile station,
interference mitigation data associated with the first and second
sets of radio resources to the first wireless AP such that
interference is mitigated.
[0028] Devices and methods are provided for using a mobile station
to mitigate interference between access points in a heterogeneous
wireless network environment.
[0029] In various embodiments, the mobile station communicates
interference mitigation data acquired from a second wireless access
point (AP) to a first wireless AP. In some embodiments the
interference mitigation data references a first and second set of
radio resources.
[0030] In various embodiments, a mobile station receives a first
resource claim for a first set of radio resources from a first
wireless access point (AP) and receives a second resource claim for
a second set of radio resources from a second AP. In one
embodiment, interference mitigation data comprising the second set
of radio resource from the second resource claim is communicated
from the mobile station to the first AP. In another embodiment,
interference mitigation data comprising a set of radio resources
from the second resource claim that conflict with radio resources
from the first resource claim is communicated from the mobile
station to the first AP.
[0031] In one embodiment, a first set of radio resources is
simultaneously claimed by both the first and second wireless AP.
The interference mitigation data, which comprises conflicting radio
resource claims from the second wireless AP, is processed by the
first wireless AP to relinquish its claim on the first set of radio
resources. The first wireless AP then assigns radio resources from
a second set of radio resources to the mobile station such that
interference with the second wireless AP is mitigated. In another
embodiment, the interference mitigation data is processed by the
first wireless AP to reduce its transmit power level (TPL) on the
radio resources assigned to the mobile station from the first set
of resources such that interference with the second wireless AP is
mitigated. In yet another embodiment, the interference mitigation
data is processed by the first wireless AP to defer its use of the
first set of radio resources until a time when interference with
the second wireless AP will be mitigated.
[0032] In some embodiments, the interference mitigation data is
processed by the first wireless AP to assign resources from the
first set of radio resources to a second mobile station such that
interference with the second wireless AP is mitigated. In various
embodiments, the mobile station receives a first resource claim for
a first set of radio resources from the first AP and receives a
second resource claim for a second set of radio resources from the
second AP. The mobile station then processes the first and second
sets of resource claim data to generate radio resource selection
data corresponding to a selection of radio resources from the first
set of radio resources, the radio resource selection data
comprising a preference assigned by the mobile station to each
selected resource. The interference mitigation data, which
comprises the radio resource selection data, is processed by the
first wireless AP to assign radio resources from the selected set
of radio resources to the mobile station according to the
preference assigned by the mobile station.
[0033] In some embodiments, the mobile station receives a resource
claim for a set of radio resources from an AP, the resource claim
comprising radio resources assigned by the AP to a plurality of
mobile stations served by the AP. In some embodiments, the mobile
station receives a resource claim for a set of radio resources from
an AP, the resource claim comprising radio resources assigned by
the AP to the mobile station. In various embodiments, a wireless
access point (AP) transmits a set of claims for radio resources,
each claim for radio resources being associated with a different
transmit power zone (TPZ). In one embodiment, the AP transmits a
first resource claim at a first transmit power level (TPL)
associated with a first TPZ and transmits a second resource claim
at a second transmit power level (TPL) associated with a second
TPZ.
[0034] In another embodiment, the AP transmits a first claim for
radio resources that comprises the identity of a first TPZ and
transmits a second claim for radio resources that comprises the
identity of a second TPZ. The AP also transmits a set of power
reference signals (PRS) wherein the AP transmits a first PRS at a
first transmit power level (TPL) associated with the first TPZ and
transmits a second PRS at a second transmit power level (TPL)
associated with the second TPZ. The mobile station detects a PRS,
identifies the associated TPZ, and matches the identity of the TPZ
with the resource claims for either the first or second TPZ.
[0035] In yet another embodiment, the AP transmits a first claim
for radio resources that comprises pathloss data associated with a
first TPZ and transmits a second claim for radio resources that
comprises pathloss data associated with a second TPZ. The AP also
transmits a power reference signal (PRS) at a TPL known to the
mobile station. The mobile station measures the Signal to
Interference-plus-Noise Ratio (SINR) of the received PRS,
calculates the pathloss of the PRS, and matches the calculated
pathloss with the pathloss data and the associated resource claim
for either the first or second TPZ.
[0036] Various illustrative embodiments of the present disclosure
will now be described in detail with reference to the accompanying
figures. While various details are set forth in the following
description, it will be appreciated that the present disclosure may
be practiced without these specific details, and that numerous
implementation-specific decisions may be made to the disclosure
described herein to achieve the inventor's specific goals, such as
compliance with process technology or design-related constraints,
which will vary from one implementation to another. While such a
development effort might be complex and time-consuming, it would
nevertheless be a routine undertaking for those of skill in the art
having the benefit of this disclosure. For example, selected
aspects are shown in block diagram and flowchart form, rather than
in detail, in order to avoid limiting or obscuring the present
disclosure. In addition, some portions of the detailed descriptions
provided herein are presented in terms of algorithms or operations
on data within a computer memory. Such descriptions and
representations are used by those skilled in the art to describe
and convey the substance of their work to others skilled in the
art.
[0037] As used herein, the terms "component," "system" and the like
are intended to refer to a computer-related entity, either
hardware, software, a combination of hardware and software, or
software in execution. For example, a component may be, but is not
limited to being, a processor, a process miming on a processor, an
object, an executable, a thread of execution, a program, or a
computer. By way of illustration, both an application running on a
computer and the computer itself can be a component. One or more
components may reside within a process or thread of execution and a
component may be localized on one computer or distributed between
two or more computers.
[0038] As likewise used herein, the term "node" broadly refers to a
connection point, such as a redistribution point or a communication
endpoint, of a communication environment, such as a network.
Accordingly, such nodes refer to an active electronic device
capable of sending, receiving, or forwarding information over a
communications channel. Examples of local area network (LAN) or
wide area network (WAN) nodes include computers, packet switches,
cable modems, Data Subscriber Line (DSL) modems, and wireless LAN
(WLAN) access points. Examples of Internet or Intranet nodes
include host computers identified by an Internet Protocol (IP)
address, routers and WLAN access points. Likewise, examples of
nodes in cellular communication include base stations, relays, base
station controllers, home subscriber servers, Gateway GPRS Support
Nodes (GGSN), Serving GPRS Support Nodes (SGSN), Serving Gateways
(SGW), and Packet Gateways (PGW).
[0039] Other examples of nodes include client nodes, server nodes,
peer nodes and access nodes. As used herein, a mobile station is a
client node and may refer to wireless devices such as mobile
telephones, smart phones, personal digital assistants (PDAs),
handheld devices, portable computers, tablet computers, and similar
devices or other user equipment (UE) that has telecommunications
capabilities. Such mobile stations may likewise refer to a mobile,
wireless device, or conversely, to devices that have similar
capabilities that are not generally transportable, such as desktop
computers, set-top boxes, or sensors. Likewise, a server node, as
used herein, refers to an information processing device (e.g., a
host computer), or series of information processing devices, that
perform information processing requests submitted by other nodes.
As likewise used herein, a peer node may sometimes serve as a
client node, and at other times, as a server node. In a
peer-to-peer or overlay network, a node that actively routes data
for other networked devices as well as itself may be referred to as
a supernode.
[0040] An access point, as used herein, refers to a node that
provides a client node access to a communication environment.
Examples of wireless access points include cellular network base
stations and wireless broadband (e.g., WiFi, WiMAX, etc) access
points, which provide corresponding cell and WLAN coverage areas.
As used herein, a macrocell is used to generally describe a
traditional wide-area cellular network cell coverage area. Such
macrocells are typically found in suburban areas, rural areas,
along highways, or in less populated areas. As likewise used
herein, a microcell refers to a cellular network cell with a
smaller coverage area than that of a macrocell. Such micro cells
are typically used in a densely populated urban area. Likewise, as
used herein, a picocell refers to a cellular network coverage area
that is less than that of a microcell. An example of the coverage
area of a picocell may be a large office complex, a shopping mall,
or a train station. A femtocell, as used herein, currently refers
to the smallest commonly accepted area of cellular network
coverage. As an example, the coverage area of a femtocell is
sufficient for homes or small businesses.
[0041] As likewise used herein, a mobile station communicating with
a wireless access point associated with a macrocell is referred to
as a "macrocell client." Likewise, a mobile station communicating
with a wireless access point associated with a microcell, picocell,
or femtocell is respectively referred to as a "microcell client,"
"picocell client," or "femtocell client."
[0042] The term "article of manufacture" (or alternatively,
"computer program product") as used herein is intended to encompass
a computer program accessible from any computer-readable device or
media. For example, computer readable media can include but are not
limited to magnetic storage devices (e.g., hard disk, floppy disk,
magnetic strips, etc.), optical disks such as a compact disk (CD)
or digital versatile disk (DVD), smart cards, and flash memory
devices (e.g., card, stick, etc.).
[0043] The word "exemplary" is used herein to mean serving as an
example, instance, or illustration. Any aspect or design described
herein as "exemplary" is not necessarily to be construed as
preferred or advantageous over other aspects or designs. Those of
skill in the art will recognize many modifications may be made to
this configuration without departing from the scope, spirit or
intent of the claimed subject matter. Furthermore, the disclosed
subject matter may be implemented as a system, method, apparatus,
or article of manufacture using standard programming and
engineering techniques to produce software, firmware, hardware, or
any combination thereof to control a computer or processor-based
device to implement aspects detailed herein.
[0044] FIG. 1 illustrates an example of a system node 100 suitable
for implementing one or more embodiments disclosed herein. In
various embodiments, the system node 100 comprises a processor 110,
which may be referred to as a central processor unit (CPU) or
digital signal processor (DSP), network connectivity interfaces
120, random access memory (RAM) 130, read only memory (ROM) 140,
secondary storage 150, and input/output (I/O) devices 160. In some
embodiments, some of these components may not be present or may be
combined in various combinations with one another or with other
components not shown. These components may be located in a single
physical entity or in more than one physical entity. Any actions
described herein as being taken by the processor 110 might be taken
by the processor 110 alone or by the processor 110 in conjunction
with one or more components shown or not shown in FIG. 1.
[0045] The processor 110 executes instructions, codes, computer
programs, or scripts that it might access from the network
connectivity interfaces 120, RAM 130, or ROM 140. While only one
processor 110 is shown, multiple processors may be present. Thus,
while instructions may be discussed as being executed by a
processor 110, the instructions may be executed simultaneously,
serially, or otherwise by one or multiple processors 110
implemented as one or more CPU chips.
[0046] In various embodiments, the network connectivity interfaces
120 may take the form of modems, modem banks, Ethernet devices,
universal serial bus (USB) interface devices, serial interfaces,
token ring devices, fiber distributed data interface (FDDI)
devices, wireless local area network (WLAN) devices, radio
transceiver devices such as code division multiple access (CDMA)
devices, global system for mobile communications (GSM) radio
transceiver devices, long term evolution (LTE) radio transceiver
devices, worldwide interoperability for microwave access (WiMAX)
devices, and/or other well-known interfaces for connecting to
networks, including Personal Area Networks (PANs) such as
Bluetooth. These network connectivity interfaces 120 may enable the
processor 110 to communicate with the Internet or one or more
telecommunications networks or other networks from which the
processor 110 might receive information or to which the processor
110 might output information.
[0047] The network connectivity interfaces 120 may also be capable
of transmitting or receiving data wirelessly in the form of
electromagnetic waves, such as radio frequency signals or microwave
frequency signals. Information transmitted or received by the
network connectivity interfaces 120 may include data that has been
processed by the processor 110 or instructions that are to be
executed by processor 110. The data may be ordered according to
different sequences as may be desirable for either processing or
generating the data or transmitting or receiving the data.
[0048] In various embodiments, the RAM 130 may be used to store
volatile data and instructions that are executed by the processor
110. The ROM 140 shown in FIG. 1 may likewise be used to store
instructions and data that is read during execution of the
instructions. The secondary storage 150 is typically comprised of
one or more disk drives or tape drives and may be used for
non-volatile storage of data or as an overflow data storage device
if RAM 130 is not large enough to hold all working data. Secondary
storage 150 may likewise be used to store programs that are loaded
into RAM 130 when such programs are selected for execution. The I/O
devices 160 may include liquid crystal displays (LCDs), Light
Emitting Diode (LED) displays, Organic Light Emitting Diode (OLED)
displays, projectors, televisions, touch screen displays,
keyboards, keypads, switches, dials, mice, track balls, voice
recognizers, card readers, paper tape readers, printers, video
monitors, or other well-known input/output devices.
[0049] FIG. 2 shows a wireless-enabled communications environment
including an embodiment of a mobile station as implemented in an
embodiment of the disclosure. Though illustrated as a mobile phone,
the mobile station 202 may take various forms including a wireless
handset, a pager, a smart phone, a personal digital assistant
(PDA). In various embodiments, the mobile station 202 may also
comprise a portable computer, a tablet computer, a laptop computer,
or any computing device operable to perform data communication
operations. Many suitable devices combine some or all of these
functions. In some embodiments, the mobile station 202 is not a
general purpose computing device like a portable, laptop, or tablet
computer, but rather is a special-purpose communications device
such as a telecommunications device installed in a vehicle. The
mobile station 202 may likewise be a device, include a device, or
be included in a device that has similar capabilities but that is
not transportable, such as a desktop computer, a set-top box, or a
network node. In these and other embodiments, the mobile station
202 may support specialized activities such as gaming, inventory
control, job control, task management functions, and so forth.
[0050] In various embodiments, the wireless network 220 comprises a
plurality of wireless sub-networks `A` 212 through `n` 218. As used
herein, the wireless sub-networks `A` 212 through `n` 218 may
variously comprise a mobile wireless access network, a wireless
local area network or a fixed wireless access network. In these and
other embodiments, the mobile station 202 transmits and receives
communication signals, which are respectively communicated to and
from the wireless network access points `A` 210 through `n` 216 by
wireless network antennas `A` 208 through `n` 214 (e.g., cell
towers). In turn, the communication signals are used by the
wireless network access points `A` 210 through `n` 216 to establish
a wireless communication session with the mobile station 202. As
used herein, the wireless network access points `A` 210 through `n`
216 broadly refer to any access point of a wireless network. As
shown in FIG. 2, the wireless network access points `A` 210 through
`n` 216 are respectively coupled to wireless sub-networks `A` 212
through `n` 218.
[0051] In various embodiments, the wireless sub-networks `A` 212
through `n` 218 are coupled to a wired network 222, such as the
Internet. Via the wireless sub-networks `A` 212 through `n` 218and
the wired network 222, the mobile station 202 has access to
information on various hosts, such as the server node 224. In these
and other embodiments, the server node 224 may provide content that
may be shown on the display 204 or used by the mobile station
processor 110 for its operations. Alternatively, the mobile station
202 may access the wireless sub-networks `A` 212 through `n`
218through a peer mobile station 202 acting as an intermediary, in
a relay type or hop type of connection. As another alternative, the
mobile station 202 may be tethered and obtain its data from a
linked device that is connected to the wireless sub-networks `A`
212 through `n` 218. Skilled practitioners of the art will
recognize that many such embodiments are possible and the foregoing
is not intended to limit the spirit, scope, or intention of the
disclosure.
[0052] FIG. 3 is a simplified block diagram of a heterogeneous
wireless network environment comprising a plurality of macro cells,
micro cells, pico cells and femto cells as implemented in
accordance with an embodiment of the disclosure. In this
embodiment, a heterogeneous wireless network environment comprises
a plurality of wireless network macro cells `X` 302, `Y` 304
through `z` 306. In this and other embodiments, each of the
wireless network macro cells `X` 302, `Y` 304 through `z` 306 may
comprise a plurality of wireless network micro cells 308, which in
turn may comprise a plurality of wireless network pico cells 310.
Likewise, the wireless network macro cells `X` 302, `Y` 304 through
`z` 306 may also comprise a plurality of individual wireless pico
cells 310.
[0053] In various embodiments, the micro cells 308 may be
associated with business or administrative entities `A` 312, `B`
314 through `n` 316, and the pico cells 310 may likewise be
associated with business or administrative entities `P` 318, `Q`
320 through `R` 322. In these various embodiments, the wireless
macro cells `X` 302, `Y` 304 through `z`, micro cells 308, and pico
cells 310 may comprise a plurality of wireless technologies and
protocols, thereby creating a heterogeneous operating environment
within the wireless network system 300. Likewise, each of the
wireless macro cells `X` 302, `Y` 304 through `z` 306, micro cells
308, and pico cells 310 comprises a corresponding wireless access
point (AP). As used herein, an AP is a generic term that broadly
encompasses wireless LAN access points, macro cellular base
stations (e.g., NodeB, eNB), micro- and pico-cells, relay nodes and
home-based femtocells (e.g., HeNB), or any telecommunications
technology operable to establish and sustain a wireless
communication session. As likewise used herein, a "cell" (or
"sector") is a portion of the coverage area served by an AP.
According, each cell has a set of radio resources that can be
associated with that cell through, for example, a unique cell
identifier.
[0054] Skilled practitioners of the art are aware that future
wireless network systems will likely rely on denser deployments of
heterogeneous network technologies such as that shown in FIG. 3 to
provide higher capacity. However, such higher capacity will, in
general, require higher signal to interference-plus-noise ratio
(SINR) over a significant percentage of a cell's coverage area. In
general, the achievement of higher SINR will require smaller cells
or, rather, operation in a smaller region of a cell when
transmitting at a given power level. Hence, the current network
model of higher power outdoor macro cells will need to be augmented
by a set of lower power indoor and outdoor micro- and pico-cells in
order to increase system capacity and mobile station
throughput.
[0055] This move towards smaller cells will significantly increase
the number of APs in the system and will also lead to significant
coverage overlap, both planned and unplanned, as shown in FIG. 3.
As a result, adjacent channel interference can occur when
overlapping cells are operating in adjacent portions of the radio
spectrum using either the same or different radio access
technologies. Likewise, co-channel interference can occur when
overlapping cells are operating in the same portion of the radio
spectrum.
[0056] While transmission and reception within a given cell will be
coordinated by its corresponding AP, operation across cell
boundaries may be un-coordinated due to the vagaries of radio
propagation, differences or incompatibilities between
administrative domains, or difficulties encountered in
communicating between APs. However, completely un-coordinated
operation may ultimately result in unacceptable levels of
interference that could negate the benefits of improved signal
levels garnered through the use of smaller cells.
[0057] Accordingly, there is a corresponding need for the
mitigation of interference to enhance performance, which requires
cooperation between the aforementioned APs. However, current
deployments may not have suitable, or for that matter any, direct
communication paths (e.g., physical backhaul) between APs. As a
result, interference mitigation cannot occur as there is no
mechanism for one AP to cooperate with another AP. Furthermore,
realization of real-time channel-dependent cooperation between
multiple APs may be unachievable if any available direct
communication paths are unable to sustain the required latency and
throughput.
[0058] Various approaches to this issue are known, including having
APs communicate either directly through physical backhaul networks
or through a centralized control structure to coordinate
communications. One iterative approach is for the AP to coordinate
mobile stations to be transmitted to and the resources to be
transmitted. Another approach is to have the AP to act as a master
manager for a set of radio resources. In one such example, a zone
of resources can be specified for coordinated transmission as
described in greater detail herein. However, this approach requires
not only the afore-mentioned direct communication between APs, but
also a means to converge mobile station selection and resource
assignment between various APs. Furthermore, this coordination is
also limited to the resources specified within the zone. Moreover,
there is the further drawback that either the communications path
or the coordination procedure, or both, is too slow to make use of
small-scale variation within the channel.
[0059] FIG. 4 is a simplified block diagram showing the detrimental
effect of co-channel inter-cell interference as mitigated in
accordance with an embodiment of the disclosure in a single
frequency network. In this embodiment, access points `A` 402, `B`
406, and `C` 410 have corresponding coverage areas `A` 404, `B`
408, and `C` 412. As shown in FIG. 4, mobile station `1` 414 is
being served by access point (AP) `A` 402 but also falls within the
coverage area of AP `B`408. Likewise, mobile station (MS) `2` 418
is being served by AP `C` 410 but also falls within the coverage
area of AP `A` 404 and AP `B` 408. As likewise shown in FIG. 4, MS
`3` 418, served by AP `A` 402, and MS `4` 420, served by AP `B`
406, are not affected by transmissions from any other AP.
[0060] Accordingly, MS `1` 414 may be affected by inter-cell
interference if its serving AP (i.e., AP `A` 402), attempts to
transmit information to MS `1` 414 when AP `B` 406 is also
attempting to transmit information to MS `4` 420. Likewise, MS `2`
418 may be affected by inter-cell interference if its serving AP
(i.e., AP `C` 410), attempts to transmit information to MS `2` 418
when either AP `A` 402 or AP `B` 406, or both, are attempting to
transmit information to the mobile stations they are serving.
[0061] Skilled practitioners of the art will recognize that
inter-cell interference can be avoided, or at least mitigated, if
the APs `A` 402, `B` 406, and `C` 410 are able to coordinate their
transmissions to ensure that each AP uses a different set of radio
resources during any downlink transmission. One known approach to
such coordination is to use an off-line configuration process to
provision each AP with the set of radio resources that it is
allowed to use. This assignment of radio resources remains in
effect until the AP is re-configured. However, this approach is not
responsive to changing interference conditions and does not take
into account the conditions seen by individual mobile stations.
[0062] Those of skill in the art will likewise be aware that
coordination in today's cellular systems is based on the premise
that the network has a global view of everything that is happening
within the coverage area and, ultimately, has total control over
everything that is happening within the coverage area. This global
view and control may be provided by centralized servers within the
radio access network (RAN) infrastructure or through peer-to-peer
communications between Access Points.
[0063] However, the validity of this assumption is questionable in
the heterogeneous wireless network environment shown in FIG. 3, due
in part to the partitioning of the network environment into
multiple administrative domains. As a result, there may be no
single network entity with a global view and with total control
over the radio environment. Furthermore, if such an entity exists,
it may not be possible to communicate between APs in different
domains. Accordingly, even within a single administrative domain,
the latency and bandwidth of the RAN backhaul network may preclude
real-time communications between APs.
[0064] FIG. 5 shows a process signal flow for mobile
station-assisted radio resource conflict resolution as implemented
in an embodiment of the disclosure to mitigate interference between
wireless access points. In various embodiments, one or more mobile
stations assist in mitigating the effects of interference by acting
as an intermediary between competing access points shown in the
heterogeneous wireless network environment of FIG. 3. In such an
environment, the mobile station (MS) may be the only entity with
visibility of all radio conditions affecting its operation at any
given time and in any given location. By observing which radio
resources have been claimed by access points covering its current
location, a MS can report conflicting claims to its serving access
point (AP) to avoid transmissions that use the same set of radio
resources.
[0065] As shown in FIG. 5, each of the APs `A` 402, `B` 406, and
`C` 408' periodically broadcasts information to all mobile stations
(e.g., MS `2` 418) within its coverage area. In this and other
embodiments, the broadcast information announces the set of radio
resources that the AP (e.g., AP `A` 402, `B` 406, and `C` 408') has
claimed for use in an upcoming transmission opportunity. For
example, in step 522, AP `A` 402 is claiming the set of resources
{R.sub.A} for use in an upcoming transmission opportunity at time
t.sub.A. Likewise, AP `B` 406 and AP `C` 408 are respectively
claiming the resources {R.sub.B} and {R.sub.C} for use at times
t.sub.B and t.sub.C, in steps 524 and 528. In this and other
embodiments, these broadcasts are not coordinated. Therefore, steps
522, 524, and 528 may occur in any order and may overlap in time
440. As shown in FIG. 4, MS `2` 418 is in a position to receive
these broadcasts from APs `A` 402, `B` 406, and `C` 408.
Alternatively, APs `A` 402, `B` 406, and `C` 408 may announce the
set of resources that they are not claiming, which would minimize
the amount of information being broadcast in a cell that is heavily
loaded.
[0066] In step 530, AP `C` 408, the serving AP for MS `2` 418,
assigns a set of resources {r.sub.2} to MS `2` 418 for use in an
upcoming transmission opportunity at time t.sub.C 442. In step 532,
using the claimed resource information received from the other APs
`A` 402 and `B` 406, MS `2` 418 sends a report to its serving AP
(i.e., AP `C` 408) indicating that a subset of the resources
{{hacek over (r)}.sub.2} assigned by AP `C` 408 conflict with the
resources claimed by one or more of the interfering APs (i.e., AP
`A` 402 and AP `B` 406) during that same transmission opportunity.
Likewise, MS `2` 418 may also indicate which resources are
currently not claimed in that transmission opportunity by any of
the AP observed by MS `2` 418. Using the feedback provided by MS
`2` 418, AP `C` 408 may adjust its resource assignments to avoid
resource conflicts with other APs `A` 402 and `B` 406 and in step
534 provide MS `2` 418 with an updated set of resources {r.sub.2}
for use at time t.sub.C 442. In step 536, at the scheduled time
t.sub.C 442, the serving AP (i.e., AP `C` 408) sends the data to MS
`2` 418 using the set of radio resources assigned at step 534.
[0067] FIG. 6 shows a process signal flow for mobile
station-assisted radio resource assignment as implemented in an
embodiment of the disclosure to mitigate interference between
wireless access points. In various embodiments, a mobile station
(MS) first observes which radio resources have been claimed by
access points covering its current location, and then reports which
resources are available to its serving access point (AP) to
minimize the number of conflicting claims for radio resources.
[0068] As shown in FIG. 6, each of the APs `A` 402, `B` 406, and
`C` 408' periodically broadcasts information to all mobile stations
(e.g., MS `2` 418) within its coverage area. In this and other
embodiments, the broadcast information announces the set of radio
resources that the AP (e.g., AP `A` 402, `B` 406, and `C` 408') has
claimed (or not claimed) in an upcoming transmission opportunity.
For example, in step 622, AP `A` 402 is claiming the set of
resources {R.sub.A} for use in an upcoming transmission opportunity
at time t.sub.A. Likewise, AP `B` 406 and AP `C` 408 are
respectively claiming the resources {R.sub.B} and {R.sub.C} for use
at times t.sub.B and t.sub.C in steps 624 and 628. In this and
other embodiments, these broadcasts are not coordinated. Therefore
steps 622, 624 and 628 may occur in any order and may overlap in
time 440. As shown in FIG. 4, MS `2` 418 is in a position to
receive these broadcasts from APs `A` 402, `B` 406, and `C`
408.
[0069] In step 630, using the claimed resource information received
from the other Access Points, MS `2` 418 sends a report to its
serving AP (i.e., AP `C` 408) describing the set of resources
{r.sub.2} that are currently not claimed in an upcoming
transmission opportunity t.sub.C by any of the APs observed by MS
`2` 418. The MS `2` 418 may further limit the set of resources
{r.sub.2} that it is reporting to those resources that provide the
best signal quality to MS `2` 418 at the current time and in the
current location. In addition, the MS `2` 418 may include a signal
quality indication for each of the resources in {r.sub.2} or may
order the resources in {r.sub.2} according to signal quality. In
step 634, using the feedback provided by MS `2` 418, AP `C` 408
assigns a set of resources {r.sub.2'} to MS `2` 418 designed to
avoid resource conflicts with other APs. At the scheduled time
t.sub.C 442 in step 636, the serving AP (i.e., AP `C` 408) sends
the data to MS-'2' 418 using the set of radio resources assigned in
step 634.
[0070] FIGS. 7a-b are a simplified block diagram of
power-controlled conflict resolution as implemented in an
embodiment of the disclosure to mitigate interference between
wireless access points. In this and other embodiments, a radio
resource is defined in terms of one or more dimensions: [0071]
Time, indicating the time at which a mobile station (MS) may begin
to use the resource and the time at which a MS must stop using that
resource; [0072] Frequency, indicating the portion(s) of spectrum
that the MS may use to transmit or receive information; [0073]
Code, indicating the encoding algorithm and parameters used to
transmit or receive information, such as Code Division Multiple
Access (CDMA) spreading code or Multiple-Input Multiple-Output
(MIMO) spatial stream matrix; and [0074] Space, indicating the
region(s) in which the MS may use the resource (e.g. geophysical
location, antenna beam, angle of arrival/departure).
[0075] Of these dimensions, space is also affected by the transmit
power. More specifically, the AP selected as the serving AP and the
set of interfering neighbor APs for a given MS will depend upon the
power level used to transmit information to and from the MS.
[0076] Skilled practitioners of the art will be familiar with an
inter-cell interference zone (ICIZ), which is a region where there
is overlapping coverage from multiple APs. FIG. 7a shows an example
of ICIZs that are created when AP `1` 702, `2` 704, and `3` 706
transmit at their maximum power level. As shown in FIG. 7a, the
ICIZs occur mostly at the edges of each cell as typified by
ICIZ.sub.1-3 708, ICIZ.sub.2-3 714, and ICIZ.sub.1-2A 710. However,
those of skill in the art will also be aware that the vagaries of
topology and clutter can affect radio frequency (RF) propagation
and produce inter-cell interference zones, such as ICIZ.sub.1-2B
712 between AP `1` 702 and AP `2` 704 that may not be constrained
to the nominal (e.g., circular) edge of a cell.
[0077] Accordingly, FIG. 7b shows an example of the ICIZs that
result when AP `1` 722 reduces its transmit power level. In this
embodiment, AP `1` 722 has reduced its transmit power to a level
where it no longer has inter-cell interference zones with its
neighboring APs (i.e., APs `2` 724 and `3` 726). As a result, only
one ICIZ (i.e., ICIZ.sub.2-3 734) is created. Furthermore, a MS
being served by AP `1` 722 within its reduced coverage region will
not report any radio resource conflicts. Accordingly, in general,
the set of conflicting resources reported by a MS can be minimized,
and the set of available resources can be maximized, if the serving
AP (e.g., AP `a` 722) adjusts its transmit power level to match the
current location of the MS. To accomplish this, an AP (e.g., AP `a`
722) is implemented in this and other embodiments to use different
transmit power levels, and at each power level, broadcasts the set
of resources it is claiming for a given transmission opportunity at
that transmit power level.
[0078] FIG. 8 shows a process signal flow for power-controlled
conflict resolution as implemented in an embodiment of the
disclosure to mitigate interference between wireless access points.
In this embodiment, access point (AP) `A` 402 is partially
interfering with mobile station (MS) `2` 418, which receives the
set of claimed resources for use at time t.sub.A broadcast in step
822 at transmit power level 1 {R.sub.A.sup.I}. However, MS `2` 418
does not receive the set of claimed resources broadcast in step 824
at transmit power level 2 {R.sub.A.sup.2}. Likewise, as shown in
FIG. 8, because MS `2` 418 does not receive the set of claimed
resources broadcast in step 826 by AP B' 406 at transmit power
levelp {R.sub.B.sup.p}, AP `B` 406 does not interfere with MS `2`
418 at that power level.
[0079] In some embodiments, the power or reliability of information
broadcast by an AP (e.g., APs `A` 402, `B` 406, and `C` 408) to all
MSs may be different from that of information transmitted by an AP
to a specific MS (e.g., MS `2` 418). Therefore, MS `2` 418 may
actually receive and decode the message broadcast in step 826 from
AP `B` 406 claiming a set of resources but may choose instead to
ignore the claims based on some signal quality metric. For example,
MS `2` 418 may ignore the claims if the Signal to
Interference-Plus-Noise Ratio (SINR) for the message claiming
{R.sub.B.sup.p}, transmitted at power level p, is below a
predetermined threshold value.
[0080] Accordingly, as shown in FIG. 8, MS `2` 418 receives the set
of claimed resources {R.sub.C.sup.K} for use at time t.sub.C
broadcast in step 828 at transmit power level k. In this and other
embodiments, these broadcasts are not coordinated. Therefore, steps
822, 824, 826 and 828 may occur in any order and may overlap in
time 440. As likewise shown in FIG. 8, AP `C` 408 assigns a set of
resources {r.sub.2.sup.k} in step 830 to MS `2` 418 for use in an
upcoming transmission opportunity at time t.sub.C 442 using
transmit power level k. Therefore, the conflict report sent by MS
`2` 418 in step 832 will be based only on the conflicts, if any,
detected in the resources {R.sub.A.sup.I} claimed by AP `A` 402 in
step 822 using transmit power level 1. The resources used by AP `A`
402 at transmit power level 2 and by AP `B` 406 at transmit power
level p do not interfere with the resources assigned to MS `2` 418
at transmit power level k. Accordingly, using the feedback provided
by MS `2` 418, AP `C` 408 may adjust its transmit power level to
avoid resource conflicts with other APs `A` 402 and `B` 406 and in
step 834 provide MS `2` 418 with an updated set of resources
{r.sub.2'} for use at time t.sub.C 442. In step 836, at the
scheduled time t.sub.C 442, the serving AP (i.e., AP `C` 408) sends
the data to MS `2` 418 using the set of radio resources assigned at
step 834.
[0081] FIG. 9 is a simplified block diagram of a mobile
station-assisted inter-access point (AP) communications environment
as implemented in accordance with an embodiment of the disclosure
to mitigate interference between wireless APs. In this and other
embodiments, the move towards smaller cells and a mixture of
heterogeneous radio access technologies increases the number of APs
within a coverage area and likewise leads to coverage overlaps,
both planned and unplanned, between cells. For example, wireless
access facilities may be owned and deployed by numerous entities
including cellular service providers, enterprise businesses,
municipal governments, local retailers and individual home owners.
With a corresponding proliferation of low power micro-, pico-, and
femto-cells, it is unlikely that a single network entity will have
a global view and total control of the overall radio environment.
In fact, it is likely that an individual mobile station (MS) may be
the only entity with viable and accurate visibility of the radio
environment in which it operates at a given location.
[0082] More specifically, communications between APs within a given
coverage area may be difficult, if not impossible, due to a number
of factors. For example, the APs may be in different Radio Access
Networks (RANs) that are owned and/or operated by different
business entities. Likewise, the APs may be in different RANs with
no communications path between each other. Conversely, the APs may
be in the same RAN but the backhaul infrastructure may not provide
a communications path between the APs. As another example, the
backhaul infrastructure may not offer the bandwidth or latency
necessary to meet inter-AP signaling requirements, or the APs may
not be able to receive radio transmissions from one another,
precluding direct communication over the air.
[0083] Therefore, the only communications path which can be
consistently relied upon is the one directly between an AP in a RAN
and a MS. By extension, the only viable communication path between
APs in the same RAN, or in different RANs, may be indirectly via a
Mobile Station that has a direct communications path with each of
the corresponding APs. Accordingly, the unique position and
capabilities of a MS is implemented in these various embodiments to
detect and coordinate the usage of radio resources amongst APs to
avoid the detrimental effects of inter-cell interference.
[0084] As shown in FIG. 9, MS `1` 902 has a direct 914
communications path to APs `A` 906, `B` 908, and `D` 910, while MS
`2` 904 has a direct 914 communications path to AP `B` 908 and `C`
912. Accordingly, interaction between APs `A` 906 and `B` 908 can
occur via MS `1` 902. In various embodiments, direct 914
communications paths may or may not exist between the APs `A` 906,
`B` 908, `C` 912, and `D` 910, such as via a backbone network.
However, this is not always the case, especially across access
network boundaries. As likewise shown in FIG. 9, the indirect 916
communication paths provided by MS `1` 902 between APs `A` 906, `B`
908, and `D` 910, and by MS `2` 904 between APs `B; 908 and `C`
912, is implicit rather than explicit. For example, if MS `1` 902
receives information from AP `A` 906, it may automatically forward
some or all of the information to AP `B` 908 or to AP `D` 910
without the need for AP `A 906 to take any action other than to
communicate with MS `1` 902. Accordingly, MS `1` 902 and `2` 904
enable the co-ordination and co-operation that may be necessary
between APs `A` 906, `B` 908, `C` 912, and `D` 910 both within and
across their various technology and administrative domains.
[0085] FIG. 10 is a simplified topological diagram showing the
implementation of downlink transmit power zones in accordance with
an embodiment of the disclosure to mitigate interference between
wireless access points. In this and other embodiments, inter-cell
interference (ICI) results when unwanted signals from neighboring
transmitters arrive at a receiver concurrently with a desired
signal from the intended transmitter. Skilled practitioners of the
art will be aware that ICI has traditionally been managed through
the use of orthogonal radio resources, differing in time, frequency
or code, in each of the neighboring cells (e.g., cell `.alpha.`
1004, `.beta.` 1006, and .gamma. 1008). Those of skill in the art
will likewise be aware that in a single frequency network, such as
Long Term Evolution (LTE) with an N=1 frequency reuse pattern,
spatial separation techniques such as beam-switching and
beam-forming may also be used to avoid co-channel interference.
Likewise, transmit power control (TPC) can also be used as a
spatial separation technique.
[0086] As shown in FIG. 10, a transmit power zone (TPZ) is that
portion of the cell coverage area that receives an acceptable
Signal to Interference-Plus Noise Ratio (SINR) when the transmitter
(e.g. AP `D` 1002) broadcasts at a given power level. As likewise
shown in FIG. 10, downlink TPZs in three cells, or sectors,
`.alpha.` 1004, `.beta.` 1006, and `.gamma.` 1008 are controlled by
AP `D` 1002. In this embodiment, cell `.alpha.` 1004 comprises TPZs
`1.1` 1110, `1.2` 1012, and `1.3` 1013, which respectively include
regions covered at transmit powers `TP.sub.1.1` 1020, `TP.sub.1.2`
1022, and `T.sub.1.3` 1024. In general, `TP.sub.1.1` 1020,
<`TP.sub.1.2` 1022, <`TP.sub.1.3` 1024.gtoreq.TP.sub.MAX such
that, in general, TPZ `1.1` 1110.OR right.TPZ `1.2` 1012.OR
right.TPZ `1.3` 1013.
[0087] However, skilled practitioners of the art will realize that
the vagaries of topology and clutter can affect radio frequency
(RF) propagation, which results in coverage holes and in coverage
"fingers" that extend beyond the nominal (e.g., circular) edge of a
zone. Accordingly, TPZs may be statically defined as part of the AP
configuration or they may be dynamically defined by the AP
according to the location of the MSs scheduled for servicing by the
AP within a given transmission time interval. Likewise, the number
of TPZs and the corresponding transmission power associated with
each TPZ can be dynamically varied from one cell to another (e.g.
cell `.beta.` 1006 and cell `.gamma.` 1008).
[0088] FIG. 11 is a simplified topological diagram showing the
implementation of inter-cell interference zones in accordance with
an embodiment of the disclosure for mitigating interference between
wireless access points. In this embodiment, access points `1` 1104,
`2` 1114, and `4` 1126 respectively comprise cells `.alpha.` 1106,
`.beta.` 1116, and `.gamma.` 1128. In turn, cell `.alpha.` 1106
comprises transmit power zones `TPZ.sub.1.1` 1108, `TPZ.sub.1.2`
1110, and `TPZ.sub.1.3` 1112. Likewise, cell `.beta.` 1116
comprises transmit power zones `TPZ.sub.2.1` 1118, `TPZ.sub.2.2`
1120, and `TPZ.sub.2.3` 1122, while cell `.gamma.` 1128 comprises
transmission power zones `TPZ.sub.4.1` 1130 and `TPZ.sub.4.2`
1132.
[0089] Skilled practitioners of the art will be aware that an
inter-cell interference zone (ICIZ), as described in greater detail
herein, likewise refers to a region where there are overlapping
transmit power zones from different cells. For example, as shown in
FIG. 11, 1136 between AP `1` 1104 and AP `2` 1114 occurs mostly at
the edges of the neighboring cells in portions of transmit power
zone `TPZ.sub.1-3` 1112 in AP `1` 1104 and in portions of
`TPZ.sub.2.3` 1122 in AP `2` 1114. Likewise, `ICIZ.sub.2-4` 1138
between AP `4` 1126 and AP `2` 1114 occurs mostly at the edges of
the neighboring cells in portions of transmit power zone
`TPZ.sub.4.2` 1132 in AP `4` 1126 and in portions of `TPZ.sub.2.3`
1122 in AP `2` 1114. The `ICIZ.sub.1-4` 1134 between AP `4` 1126
and AP `1` 1104 likewise occurs mostly at the edges of the
neighboring cells in portions of transmit power zone `TPZ.sub.4.2`
1132 in AP `4` 1126 and in portions of `TPZ.sub.1.3` 1112 in AP `1`
1104.
[0090] However, skilled practitioners of the art will be aware that
the vagaries of topology and clutter can affect RF propagation and
produce inter-cell interference zones that may not be constrained
to the nominal (e.g., circular) edge of a cell. For example, as
shown in FIG. 11, `ICIZ.sub.1-2B` 1142 represents a coverage
overlap between `TPZ.sub.2.2` 1120 in AP `2` 1114 and `TPZ.sub.1.3`
1112 in AP `1` 1104 where the coverage of TPZ.sub.1.3 1112 has
extended beyond its nominal (e.g., circular) edge due to the local
radio frequency (RF) propagation environment. Those of skill in the
art will likewise realize that successive underlays involving
combinations of micro-, pico- and femto-cells may likewise result
in an inter-cell interference zone that encompasses an entire cell.
For example, as shown in FIG. 11, AP `3` 1124 is a microcell that
is completely overlaid by cell `.beta.` 1116 AP `2` 114.
Accordingly, `ICIZ.sub.2-3` 1140 between AP `2` 1114 and AP `3`
1124 encompasses all of the coverage area of AP `3` 1124 and
portions of `TPZ.sub.2.2` 1120 and `TPZ.sub.2.3` 1122 in AP `2`
1114.
[0091] FIG. 12 is a simplified topological diagram showing the
implementation of mobile station serving and contending cell sets
in accordance with an embodiment of the disclosure for mitigating
interference between wireless access points. In this embodiment,
access points `1` 1104, `2` 1114, and `4` 1126 respectively
comprise cells `.alpha.` 1106, 1116, and `.gamma.` 1128. In turn,
cell `.alpha.` 1106 comprises transmit power zones
`TPZ.sub.1.1'1108, `TPZ.sub.1.2` 1110, and `TPZ.sub.1.3` 1112.
Likewise, cell `.beta.` 1116 comprises transmit power zones
`TPZ.sub.2.1` 1118, `TPZ.sub.2.2` 1120, and `TPZ.sub.2.3` 1122,
while cell `.gamma.` 1128 comprises transmission power zones
`TPZ.sub.4.1` 1130 and `TPZ.sub.4.2` 1132.
[0092] As shown in FIG. 12, the inter-cell interference zone (ICIZ)
`ICIZ.sub.1-2A` 1136 between AP `1` 1104 and AP `2` 1114 occurs
mostly at the edges of the neighboring cells in portions of
transmit power zone `TPZ.sub.1.3` 1112 in AP `1` 1104 and in
portions of `TPZ.sub.2.3` 1122 in AP `2` 1114. Likewise,
`ICIZ.sub.2-4` 1138 between AP `4` 1126 and AP `2` 1114 occurs
mostly at the edges of the neighboring cells in portions of
transmit power zone `TPZ.sub.4.2` 1132 in AP `4` 1126 and in
portions of `TPZ.sub.2.3` 1122 in AP `2` 1114. The `ICIZ.sub.1-4`
1134 between AP `4` 1126 and AP `1` 1104 likewise occurs mostly at
the edges of the neighboring cells in portions of transmit power
zone `TPZ.sub.4.2` 1132 in AP `4` 1126 and in portions of
`TPZ.sub.1.3` 1112 in AP `1` 1104.
[0093] As likewise shown in FIG. 12, `ICIZ.sub.1-2B` 1142
represents a coverage overlap between `TPZ.sub.2.2` 1120 in AP `2`
1114 and `TPZ.sub.1.3` 1112 in AP `1` 1104 where the coverage of
`TPZ.sub.1.3` 1112 has extended beyond its nominal (e.g., circular)
edge due to the local radio frequency (RF) propagation environment.
Likewise, AP `3` 1124 is a microcell that is completely overlaid by
cell `.beta.` 1116 AP `2` 114. Accordingly, `ICIZ.sub.2-3` 1140
between AP `2` 1114 and AP `3` 1124 encompasses all of the coverage
area of AP `3` 1124 and portions of `TPZ.sub.2.2` 1120 and
`TPZ.sub.2.3` 1122 in AP `2` 1114.
[0094] As shown in FIG. 12, mobile station (MS) `a` 1250 is
operating within `TPZ.sub.1.2` 1110 of cell `a` 1106, while MS `b`
1252 is operating within `ICIZ.sub.1-2A` 1136, and MS `c` 1254 is
operating within `TPZ.sub.2.2` 1120 of cell `.beta.` 1116 as well
as within `ICIZ.sub.2-3` 1140. Likewise MS `d` 1256 is operating
within `TPZ.sub.2.2` 1120 of cell `.beta.` 1116 as well as within
`ICIZ.sub.2-3` 1140, while MS `e` 1258 is operating within
`TPZ.sub.2. 2` 1120 of cell `.beta.` 1116 and MS `f` 1260 is
operating within `TPZ.sub.4.2` 1132 of cell `.gamma.` 1128. As
likewise shown in FIG. 12, MS `g` 1262 is operating within
`ICIZ.sub.2-4` 1138, while MS `h` 1264 is operating within
`ICIZ.sub.1-4` 1134. Likewise, MS `i` 1266 is operating within
`TPZ.sub.4.2` 1132 of cell `.gamma.` 1128 and MS `k` 1268 is
operating within `ICIZ.sub.2-4` 1138.
[0095] Skilled practitioners of the art will be aware that a mobile
station's serving cell set (MSCS) is the collection of one or more
cells where the mobile station (MS) is actively exchanging, or
planning to exchange, traffic with those cells. This includes the
cell that is currently serving the MS as well as any cells that are
handover targets. For example, in this embodiment, MS `g` 1262 is
in transition from `TPZ.sub.4.2` 1132 in cell `.gamma.` 1128 of AP
`4` 1126 to `TPZ.sub.1.3` 1112 in cell `.alpha.` 1106 of AP `1`
1104. Accordingly, the MSCS for MS `g` 1262 has two members--cell
4-.gamma., its serving cell, and cell 1 .alpha., its target
cell.
[0096] Accordingly, skilled practitioners of the art will recognize
that a mobile station cell coverage zone (MCCZ) is the collection
of transmit power zones that provide coverage to the MS within each
cell of the MSCS. Likewise, in general, the MCCZ will include the
TPZ with the minimum power to reach the MS as well as the TPZs
operating at a higher power transmit power level. For example, as
shown in FIG. 12, MS `a` 1250 operating within `TPZ.sub.1.2` 1110
in cell `.alpha.` 1106 of AP `1` 1104 will have a MCCZ that
includes cell `.alpha.` 1106 of AP `1` 1104 as its current serving
cell and a cell coverage zone in cell 1- a that includes
`TPZ.sub.1.2` 1110 as well as `TPZ.sub.1.3` 1112. However,
`TPZ.sub.1.1` 1108 would not be a member of the MCCZ for MS `a`
1250 due to its lower transmit power. From the foregoing, it will
be apparent that the cell MCCZ for a given MS is based on the
ability of the MS to detect and decode a signal above a certain SNR
threshold. This, in turn, is based on the combination of transmit
power from an AP and the sensitivity of the receiver implemented
within the MS.
[0097] Those of skill in the art will recognize that a mobile
station contending cell set (MCCS) is the collection of one or more
cells where the MS is able to decode the cell control information
broadcast from an AP. As such, the MCCS comprises members of the
MSCS as well as interfering cells from neighboring APs. Likewise,
the MS's ICIZ is represented by the overlapping transmit power
zones of the MCCS. In various embodiments, the MS may not be
actively exchanging, or planning to exchange, traffic with all of
the cells in its MCCS, therefore the MCCS may include cells that
are not members of the MS's serving cell set.
[0098] In the example of FIG. 12, MS `c` 1254 will have a serving
cell set that includes the omni-directional cell of AP `3` 1124 as
its serving cell and a cell coverage zone in AP `3` 1124 that
includes its corresponding single transmit power zone. Accordingly,
MS `c` 1254 will have AP `2` 1114 and AP `3` 1124 in its contending
cell set and will be in `ICIZ.sub.2-3` 1140, which includes
`TPZ.sub.2.2` 1120 and TPZ.sub.2.3' 1122 of AP `2` 1114 and the
single transmit power zone of AP `3` 1124. Skilled practitioners of
the art will likewise realize that the vagaries of topology and
clutter may produce propagation and shadowing effects that produce
coverage holes within a cell and extend coverage beyond the nominal
(e.g., circular) edge of a cell. For example, as likewise shown in
FIG. 12, a MS `d` 1256 operating within `ICIZ.sub.1-2B` 1142 may
have a MCCS with cell `.beta.` 1116 of AP `2` 1114 as its current
serving cell and a cell coverage zone in cell 2-.beta. that
includes an interior transmit power zone, `TPZ.sub.2.2' 1120,
rather than a cell edge transmit power zone. However, MS `d` 1256
will have cell `.alpha.` 1106 of AP `1` 1104 and cell `.beta.` 1116
of AP `2` in its MCCS and will be within `ICIZ.sub.1-2B` 1142,
which that includes both `TPZ.sub.1.3` 1112 and `TPZ.sub.2.2`
1120.
[0099] FIG. 13 shows a process signal flow for interference
mitigation procedures as implemented in an embodiment of the
disclosure to mitigate interference between wireless access points.
In various embodiments, an access point (AP) periodically
broadcasts during time 1340 a set of power reference signals (PRS)
for each cell at the highest power level allowed for the cell or at
some reduced power level determined by administrative policies or
power management algorithms. In this embodiment, AP `2` 1114
broadcasts a set of PRS {PRS.sub.2} in step 1322 at transmit power
(TP) level TP.sub.2 that defines the extent of coverage for this
cell.
[0100] In this and other embodiments, each mobile station (MS),
such as MS `d` 1256, is responsible for using the PRS to identify
the transmit power zone (TPZ) in which it is currently operating.
Likewise, the MS identifies the time and frequency radio resources
assigned to the set of PRS using cell control information, such as
a Long Term Evolution (LTE) System Information Block, that is
periodically broadcast throughout the cell by an AP. In these
various embodiments, coordination mechanisms between APs (e.g.
based on the physical cell ID) may be required to ensure that
reference signals in neighboring cells can be distinguished, such
as by using an orthogonal set of resources. Likewise, the
functionality of the power reference signals may be combined with
other information broadcast by the AP in some radio access
technologies, such as in the Long Term Evolution (LTE) Physical
Broadcast Channel (PBC).
[0101] In this embodiment, the MS `d` 1256 performs Signal to
Interference-plus-Noise Ratio (SINR) measurements on the power
reference signals from each of the cells (e.g., AP `2` 1114) in its
serving set. The MS `d` 1256 then reports the received power
reference signal strength {RPRSS.sub.D} it has measured to AP `2`
1114 in step 1322 when the SINR of the power reference signal is
above an acceptable value. In turn, AP `2` 1114 computes the amount
of path loss encountered by the MS in its current location, which
is the difference between the transmit power level (TP.sub.2) and
the reported RPRSS for each PRS, and correlates the losses reported
by multiple MSs to dynamically group them into transmit power zones
for radio resource scheduling.
[0102] In addition to the power reference signals, the AP for each
cell (e.g., AP `1` 1104 and AP `2` 1114) also periodically
broadcasts a claimed zone resource map (CZRM) for each transmit
power zone (TPZ). The CRZM indicates which radio resources, such as
Orthogonal Frequency-Division Multiplexing (OFDM) sub-carriers it
has claimed for use in an upcoming transmission opportunity (TXOP).
As shown in FIG. 13, AP `1` 1104 and AP `2` 1114 respectively
broadcast such a CRZM signal in steps 1326 at time t.sub.1 1342 and
step 1328 at time t.sub.2 1344. Logically, the CZRM contains
information for each radio resource in the uplink direction, the
downlink direction, or both, indicating whether that resource has
or has not been claimed by this AP for use in that TXOP.
[0103] Those of skill in the art will be aware that a transmission
opportunity is a sequence of one or more transmission time
intervals (TTIs) in an upcoming frame or sequence of frames. The
resources being claimed in that TXOP may be committed resources
that have already been scheduled by the AP or they may be
anticipated resources that the AP may be trying to reserve as a
block for later allocation to individual Stations. Committed
resources will reflect actual resource requirements within that
TXOP while anticipated resources will reflect a forecast of
resource requirements within that TXOP.
[0104] In this and other embodiments, each AP (e.g. AP `1` 1104 and
`2` 1114) is responsible for ensuring that there are no radio
resource assignment conflicts across the transmit power zones of
its own cells. For example, in FIG. 12, AP `2` 1114 will ensure
that resources assigned for use in `TPZ.sub.2 1118 are not
simultaneously assigned for use in `TPZ.sub.2.3` 1122 within a
given transmission time interval. In addition, as described in
greater detail herein, an AP may receive reports from its
respective MSs of resource claims made in neighboring cells that
can be used by the AP to minimize radio resource assignment
conflicts.
[0105] Since resources assigned for use in an inner (e.g., lower
power) TPZ will not be simultaneously used in an outer (e.g., high
power) TPZ within the same cell, APs can claim resources in the TPZ
of an edge region without fear of conflict if they know that those
resources have already been committed for use by a neighboring AP
in one of its non-overlapping inner TPZs. Therefore, the CZRM for a
transmit power zone indicates how each radio resource in the cell
has been claimed by the controlling AP relative to that TPZ as
follows: [0106] Not claimed. The resource has not been claimed for
use within this cell. However, the Access Point may subsequently
claim this resource if needed to support instantaneous demand from
its served MSs or to avoid resource conflicts with neighboring
cells. [0107] Claimed in a lower powered TPZ. The resource has been
claimed for use in a lower-powered TPZ within this cell, therefore
the AP will not make a subsequent claim for this resource within
this TPZ. [0108] Claimed in a higher powered TPZ. The resource has
been claimed for use in a higher-powered TPZ within this cell,
therefore the AP will not make a subsequent claim for this resource
within this TPZ. However, a neighbouring cell that attempts to use
this resource may encounter increased interference. [0109] Claimed
in this TPZ. The resource has been claimed for use within this TPZ
The AP (e.g., AP `2` 1114) controlling a cell then sends in step
1330 a mobile station resource map (MRM) to each MS (e.g. MS `d`
1256) that require radio resources. The MRMs indicate which
resources (e.g. OFDM sub-carriers) it has tentatively scheduled for
use by that MS (e.g., MS `d` 1256) in an upcoming transmission
opportunity. Those of skill in the art will realize that the MRM is
a set of potential radio resources and may not reflect the actual
resources subsequently assigned to the MS (e.g., MS `d` 1256)
during that transmission opportunity. For example, the MRM may
identify the sub-band(s) from which resources will be allocated,
while the resources actually scheduled for use by the MS in that
TXOP may be a subset of those resources.
[0110] When a MS determines that it is operating in an inter-cell
interference zone (ICIZ), it compares the claimed zone resource
maps from each AP in its contending cell set to the MRM received
from its serving AP. In this and other embodiments, AP broadcasts
may not be synchronized in the time domain. Therefore, the TXOP
reference in a CZRM is relative to the originating AP. Before
comparing MRMs, the MS must time-align the TXOP reference in the
MRM with the TXOP reference in the CZRMs from the neighboring
cells.
[0111] If the MS (e.g., MS `d` 1256) finds that resources allocated
in the MRM conflict with resources claimed in one or more of the
CZRMs, then the MS sends a resource contention report (RCR) to its
serving AP (e.g., AP `2` 1114) in step 1332 indicating which
resources are being contended and providing a set of alternate
resources that are not in contention. At the time of the designated
TXOP, the serving AP (e.g., AP `2` 1114) in step 1334 may avoid
potential interference by not scheduling the use of the contended
resources in that TPZ in that TXOP. The serving AP (e.g., AP `2`
1114) may either allocate alternate resources to the MS (e.g., MS
`d` 1256) in that TXOP or re-schedule resources for the MS to a
later TXOP. However, the serving AP (e.g., AP `2` 1114) may use the
contended resources in a different TPZ during that TXOP if no
conflicts are reported in that TPZ.
[0112] In step 1330, the serving AP (e.g., AP `2` 1114) may also
send a MRM to a MS that only indicates the transmission opportunity
that the serving AP has tentatively scheduled for use by that MS.
Using the CZRMs received from neighboring cells in step 1326 at
t.sub.1 1342, and signal quality measurements made by the MS (e.g.,
MS `d` 1256), the RCR sent by the MS in step 1332 provides the
serving AP with a selection of radio resources within that TXOP
that are most suitable for use by the MS. At step 1334, the serving
AP (e.g., AP `2` 1114) assigns radio resources to the MS (e.g., MS
`d` 1256) based on the selections made by that MS.
[0113] In step 1330, the serving AP (e.g., AP `2` 1114) may also
broadcast a MRM to a group of Mobile Stations (e.g. all MSs of a
certain class or all MSs within a particular TPZ) identifying some
or all of the resources in a TXOP that the AP is claiming as a
block in anticipation of the group's resource requirements. This
block may include all of the radio resources within a TXOP or it
may include a subset of resources from multiple sub-bands to
provide the serving AP (e.g., AP `2` 1114) with options for
responding to frequency-selective fading. The RCRs sent by
individual MSs at step 1332 provide the AP with information on
which radio resources within the block are most suitable for use by
the MS (e.g., MS `d` 1256). In step 1334, the AP (e.g., AP `2`
1114) schedules the use of resources within this block and assigns
them to individual MSs within the group, providing the serving AP
with greater flexibility in exploiting the diversity of channel and
interference conditions experienced by MSs within the group when
trading-off the demands of individual MS against the availability
of resources. Then in step 1336, the serving AP (e.g., AP `2` 1114)
sends the data to the MS (e.g., MS `d` 1256) using the set of radio
resources assigned in step 1334.
[0114] FIG. 14 is a simplified block diagram of a resource claims
and contention resolution process as implemented in an embodiment
of the disclosure to mitigate interference between wireless access
points. In this and various other embodiments, the CZRM broadcast
by an AP for a transmit power zone indicates how each radio
resource in the cell has been claimed by the AP relative to the TPZ
referenced by the CZRM: [0115] Resource claimed by this AP in a
lower powered TPZ, with a CZRM value of `00`; [0116] Resource not
claimed by this AP, with a CZRM value of `01`; [0117] Resource
claimed by this AP in this TPZ, with a CZRM value of `10`; [0118]
Resource claimed by this AP in a higher powered TPZ, with a CZRM
value of `11`.
[0119] In this and various other embodiments, a mobile station (MS)
includes the maximum value of the claims for each radio resource,
across all overlapping transmission opportunities when it sends a
resource contention report (RCR) to its serving AP. At the time of
a designated transmission opportunity (TXOP), the serving access
point (AP) may attempt to minimize potential interference by
selecting resources for assignment to the mobile station in the
following order of preference: [0120] Claimed in lower powered TPZ;
[0121] Not claimed; [0122] Claimed in this TPZ; [0123] Claimed in
higher powered TPZ.
[0124] For example, MS `d` 1256 in FIG. 12 is located in
`TPZ.sub.22` 1120, where it is being served by cell `.beta.` 1116
of AP `2` 1114. However, it is experiencing interference from cell
`.alpha.` 1106 of AP `1` 1104 in `TPZ.sub.1.3` 1112. As shown in
FIG. 14:
[0125] In step `1` 1404, at time t.sub.1, the interfering AP `1`
1104 broadcasts a claimed zone resource map .sub.@tiCZRM.sub.1.3
1406 for `TPZ.sub.1.3` 1112, indicating which radio resources 1418
it is planning to use within cell `.alpha.` 1106 in two upcoming
transmission opportunities starting at times t.sub.1|k
(TXOP.sub.t1|k 1420) and t.sub.1|k|1 (TXOP.sub.t1+k+11422).
[0126] In step `2` 1410, at time t.sub.2, the serving AP `2` 1114
sends a mobile station resource map .sub.@t2MRM.sub.d 1412 to MS
`d` 1256, indicating the set of resources to be assigned to MS `d`
1256 in an upcoming transmission opportunity starting at time
t.sub.2+k (TXOP.sub.t2+k 1414). It will be appreciated that the
time references or frame sequence numbers used in CZRM 1406 and MRM
1412 are relative to AP `1` 1104 and AP `2` 1114 respectively and
may not be synchronized between AP `1` 1104 and AP `2` 1114.
[0127] In step `3` 1424, the transmissions of AP `1` 1104 and AP
`2` 1114 may not be frame aligned when received by MS `d` 1256.
Therefore, MS `d` 1256 may notice a difference in time (at) 1416
between the start of a TXOP from AP `1` 1104 and the start of a
corresponding TXOP from AP `2` 1114. As a result, it is possible
that transmissions from AP `1` 1104 in two adjacent TXOPs 1420 and
1422 will interfere with a transmission 1414 from AP `2` 1114.
[0128] In step `4`, at some time before the scheduled transmission
opportunity at t.sub.2+k (e.g., at t.sub.2-k-j), MS `d` 1256 sends
a resource contention report t.sub.2+k-j RCRd 1430 to AP `2` 1114
that reflects the claimed resources in all of the overlapping TXOPs
from all of the interfering APs in the ICIZ of MS `d` 1256.
[0129] In this and other embodiments, the contention report
constructed by MS `d` 1256 may include its preference 1428 for each
radio resource 1418 where the preference level ranges from "most
preferred" (value 1) to "least preferred" (value 4). The preference
level 1428 may be based on the maximum value of the claims from AP
`1` 1104 in TXOP.sub.t1+k 1420 and TXOP.sub.t1+k+1 1422 and on
signal quality measurements made by MS `d` 1256. More specifically,
in this example, the report indicates that one of the radio
resources 1418 `R.sub.2` intended for use by MS `d` 1256 has also
been claimed by another AP in that TXOP, but in a lower-power TPZ,
thus making it a preferred 1428 resource for use by MS `d` 1256.
Accordingly, the other radio resource 1418 `RR.sub.3` intended for
use by MS `d` 1256 is currently not claimed in one of the
overlapping TXOPs. However, it is still subject to use within the
contending cell, thus making it a less preferred 1428 radio
resource 1418 for use by MS `d` 1256. When radio resources 1418 for
TXOP.sub.t2+k 1414 are finally scheduled by AP `2` 1114, it may
choose to continue to use radio resources 1418 `RR.sub.2` and
`RR.sub.3` on the assumption that there will be minimal
interference from the neighboring cell. Conversely, it may attempt
to use preferred 1428 radio resources 1418 `RR.sub.2` and
`RR.sub.n-2` of MS `d` 1256 in an attempt to select the resources
with the least interference.
[0130] Alternatively, AP `2` 1114 may defer transmissions and
assign radio resources 1418 to MS `d` 1256 in a different
transmission time interval. The decision of whether to defer
transmission may be based on the nature of the traffic scheduled
for transmission to MS `d` 1256 (e.g. how close is the queued
information to its deadline) and may also be based on additional
information provided by MS `d` 1256 (e.g. that the resources
claimed for a later TXOP indicate that additional resources are
becoming available).
[0131] The serving AP `2` 1114 may also defer to the interfering AP
`1` 1104 and avoid assignment of the resources identified in the
RCR for some period of time after the target transmission
opportunity TXOP.sub.t2+k 1414. After that deferral period has
elapsed (e.g. at TXOP.sub.t2+k+n), AP `2` 1114 can attempt to
schedule use of the previously contended radio resources 1418 to
determine if they are still in use by AP `1` 1104 in the ICIZ. The
decision on whether or not to defer to another AP may be based on a
priority that is assigned to each cell in an AP or that is derived
from a known parameter (e.g. Physical Cell ID).
[0132] In one embodiment, "busy tones" (i.e., sub-carriers) of an
Orthogonal Frequency-Division Multiplexing (OFDM) symbol are used
to claim resources rather than a control message to announce the
planned use of radio resources through a claimed zone resource map
(CZRM). In this embodiment, the AP for each cell periodically
broadcasts an OFDM symbol with at least one reference sub-carrier
of an OFDM symbol (i.e. a tone) in each resource block that is
being claimed in an upcoming TXOP. The OFDM symbol comprises the
claimed zone resource symbol (CZRS) in which power is applied to
the reference sub-carriers at the transmit power level for the
corresponding transmit power zone. The reference sub-carriers may
also be pre-coded or spatially multiplexed using the same
parameters that will be used for data transmission during the
upcoming transmission opportunity. The other tones in the resource
block may be used for other purposes (e.g. for transmitting
information to mobile stations).
[0133] If the MS finds that resources allocated in its MRM conflict
with resources claimed in the CZRS from one or more of neighboring
cells, the MS sends a RCR to its serving AP indicating which
resources are in contention and providing an alternate set of
resources that are not. The RCR may also be an OFDM symbol in which
power is applied to each reference sub-carrier that is being
claimed by at least one of the neighboring cells in the upcoming
TXOP.
[0134] In an embodiment previously described in greater detail
herein, the MS provides its serving AP with the set of radio
resources claimed by a neighboring cell only when the MS detects a
conflict with the resources assigned by its serving AP. In another
embodiment, the MS acts as an over-the-air (OTA) relay for the
types of control messages typically exchanged over the interface
between APs in the backhaul network, an interface such as the 3GPP
LTE X2 interface.
[0135] In this embodiment, each AP periodically transmits a CZRM
indicating the radio resources that it plans to use in an upcoming
TXOP. When a MS receives a CZRM from a neighboring cell, it
forwards that information to its serving AP. The APs then adjust
their CZRM based on claims from other cells. For example, radio
resources could be pre-arranged into a set of resource groups.
Likewise, each cell may be given preferred access to a resource
group based, for example, on its physical cell ID such that the
order of preference will be different for different resource
groups, thereby ensuring that no cell can be starved for resources.
Accordingly, if an AP determines that a neighboring cell has
preferred access to a set of contended resources, it defers to the
neighbor and releases its claim to the resources. Over time, the
neighboring cells will converge on a partitioning of radio
resources based on resource demands and on the relative preference
levels of the cells.
[0136] In an embodiment previously described in greater detail
herein, an AP broadcasts a set of power reference signals (PRS) for
each of its associated cells and uses the received power reference
signal strength (RPRSS) reported by a MS to determine its
corresponding path loss and transmit power zone (TPZ). In another
embodiment, the AP associated with each cell periodically
broadcasts a different set of PRS for each TPZ such that the power
level of the PRS defines the extent of the TPZ. For example, in
FIG. 11, PRS.sub.2.3 is transmitted at power level TP.sub.2.3 and
defines the extent of `TPZ .sub.2.3` 1122. Accordingly, lower
transmit power levels are targeted at MSs that are closer to the AP
and they may not be received by MSs further from the AP or in
shadowed areas of the cell.
[0137] In this embodiment, each MS is responsible for using the PRS
to determine the collection of TPZs in which it is currently
operating. A MS identifies the time and frequency radio resources
assigned to power reference signals using cell control information
(e.g. LTE System Information Block) that is periodically broadcast
throughout the cell by an AP. Coordination mechanisms between APs
(e.g. based on the Physical Cell ID) are required to ensure that
reference signals in neighboring cells use an orthogonal set of
resources. The MS performs SNR measurements on the PRS from the
cells in its serving set and deems itself to be covered by those
TPZs where the SNR of the power reference signal is above an
acceptable value. The MS (e.g., MS `d` 1256 in FIG. 12) then
provides feedback to each cell in its serving cell set (MSCS) to
identify the TPZs covering it within each cell. In this and other
embodiments, the feedback may include the received power level of
the PRS, allowing the AP to dynamically adjust the number, and
extend, of each of the TPZs.
[0138] In an embodiment previously described in greater detail
herein, an AP broadcasts a set of PRS for each cell and uses the
RPRSS reported by a MS to determine its corresponding path loss and
TPZ. In this embodiment, the AP broadcasts a different set of PRS
for each TPZ in each cell such that the power level of the PRS
defines the extent of the TPZ. In another embodiment, an AP
broadcasts one set of power reference signals for each cell and
also broadcasts cell control information (e.g. in the LTE System
Information Block) that defines the number of TPZs in the cell and
the received power reference signal strengths (RPRSS) that define
the boundaries of each TPZ. The MS then performs measurements on
the PRS received from the cell to determine the RPRSS at its
location. The MS then compares its measured RPRSS with the entries
in the list broadcast in the cell control information and reports
the identity of the TPZ (e.g. the index within the list) associated
with the matching entry to the serving AP.
[0139] In an embodiment previously described in greater detail
herein, an AP transmits a separate claimed zone resource map (CZRM)
for each transmit power zone (TPZ) in a cell, which is broadcast at
the transmit power level associated with that TPZ. FIG. 15 is a
simplified block diagram of a compact claimed zone resource map
(CCZRM) as implemented in an alternate embodiment of the disclosure
to mitigate interference between wireless access points.
[0140] In this embodiment, a single compact claimed zone resource
map (CCZRM) for each transmission opportunity, such as
`CCZRM.sub.1@TXOP.sub.t+k` 1504, is used within each cell,
broadcast by the AP at the highest power level allowed for that
cell, or alternatively, at some reduced power level determined by
administrative policies or power management algorithms. Logically,
the CCZRM contains an entry for each radio resource 1502 in the
uplink direction, the downlink direction, or both, indicating the
transmission power zone(s) where the radio resource 1502 will be
used within the cell in the upcoming transmission opportunity.
[0141] In one embodiment, a single set of power reference signals
(PRS), such as `PRS.sub.1` 1506, is used with transmission power
zone(s) defined by received power reference signal strength (RPRSS)
thresholds. In this embodiment, each entry of the CCZRM contains
either an indication that the radio resource 1502 is unclaimed or,
if it is claimed, the identifier for the transmission power zone
(TPZ) where the radio resource 1502 will be used. In another
embodiment, TPZ-specific PRS are used. In this embodiment, each
entry of the CCZRM contains a reference 1508 to the PRS that
defines the extent of the TPZ where the radio resource 1502 will be
used. If the radio resource 1502 is not being claimed by this AP in
the upcoming TXOP, there is no reference to a corresponding
PRS.
[0142] For example, as shown in FIG. 15, radio resource 1502
`R.sub.4` has been claimed by AP `1` 1104 for use in an upcoming
transmission opportunity TXOP.sub.t+k. This radio resource 1502
will be used within the TPZ defined by the power reference signal
at `index 3` within the `PRS.sub.1` 1506 set used by AP `1` 1104.
Accordingly, the PRS at `index 3` is transmitted at power level `TP
1.2`, thereby defining the extent of `TPZ.sub.1.2`. Likewise, radio
resource 1502 `RR.sub.n-2` has also been claimed for use in
`TPZ.sub.1.2` (`index 3`) while radio resources 1502`RR.sub.3` and
`RR` been claimed for use in `TPZ.sub.1.3 index j-2`) and radio
resource 1502 `RR.sub.2` has been claimed for use in `TPZ.sub.1.1`
(`index 1`).
[0143] In various embodiments previously described in greater
detail herein, an AP is allowed to claim radio resources in the
uplink direction, the downlink direction, or both. However, skilled
practitioners of the art will be aware that the region covered by a
mobile station's uplink transmission may be different from the
region covered by an AP's downlink transmission, which could
possibly affect the claiming of uplink resources and the reporting
of those claims.
[0144] However, a mobile station (MS) may not be able to receive
transmissions directly from another MS in order to detect uplink
interference from other mobile stations. This is always the case
when frequency division duplexing (FDD) is used on the radio link.
Likewise, this is sometimes the case when time division duplexing
(TDD) is used, such as when MSs are "hidden" from each other,
either by topology or when searching for the signal from another,
possibly unknown, MS is impractical.
[0145] FIG. 16 is a simplified topological diagram showing the
effect of an interfering mobile station inside of an inter-cell
interference zone (ICIZ) in accordance with an embodiment of the
disclosure for mitigating interference between wireless access
points. In this embodiment, AP `2` 1614 comprises cell `.beta.`
1616, which in turn comprises transmit power zones `TPZ.sub.2 1618,
`TPZ.sub.2.2` 1620, and `TPZ.sub.2.3` 1622. Likewise, AP `4` 1626
comprises cell `.gamma.` 1628, which further comprises transmission
power zones `TPZ.sub.4 1630 and `TPZ.sub.4.2` 1632. As shown in
FIG. 16, `ICIZ.sub.2-4` 1638 between AP `4` 1626 and AP `2` 1614
occurs mostly at the edges of the neighboring cells in portions of
transmit power zone `TPZ.sub.4.2` 1632 in AP `4` 1126 and in
portions of `TPZ.sub.2.3` 1622 in AP `2` 1614. As likewise shown in
FIG. 16, MS `k` 1656 is operating within `ICIZ.sub.2-4` 1638' while
MS `i` 1654 is operating within `TPZ.sub.4.2` 1632, which
contributes to the `ICIZ.sub.2-4` 1638. However, MS `i` 1654 is not
operating within `ICIZ.sub.2-4` 1638 itself
[0146] Since MS `i` 1654 is outside of the `ICIZ.sub.2-4` 1638, and
beyond the range of AP `2` 1614, it is unable to report AP `2` 1614
claims for `TPZ.sub.2.3` 1622 to AP `4` 1626. However, MS `k` 1656
can report AP `4` 1626 claims for `TPZ.sub.4.2` 1632 to AP `2`
1614. As shown in FIG. 16, the region covered by the uplink
transmission from MS `i` 1654 only extends to its serving AP, AP
`4` 1626. However, the region covered by the uplink transmission
from MS `k` 1656 extends to both its serving AP, AP `2` 1614 and to
its neighboring AP, AP `4` 1626. Therefore, uplink resources
assigned by AP `4` 1626 to MS T 1654 should not be used by MS `k`
1656 as uplink transmissions from MS `k` 1656 would also be
received as interference by AP `4` 1626. This issue is successfully
resolved in various embodiments, described in greater detail
herein, by MS `k` 1656 sending a resource contention report to AP
`2` 1614, its serving AP, thereby causing it to avoid use of the
contended radio resources.
[0147] FIG. 17 is a is a simplified topological diagram showing a
mobile station as implemented in accordance with an embodiment of
the disclosure for calculating path loss to mitigate interference
between wireless access points. In this embodiment, AP `2` 1614
comprises cell `.beta.` 1616, which in turn comprises transmit
power zones `TPZ.sub.21` 1618, `TPZ.sub.22` 1620, and `TPZ.sub.23`
1622. Likewise, AP `4` 1626 comprises cell `.gamma.` 1628, which
further comprises transmission power zones `TPZ.sub.4` 1630 and
`TPZ.sub.42` 1632. As shown in FIG. 17, `ICIZ.sub.2-4` 1638 between
AP `4` 1626 and AP `2` 1614 occurs mostly at the edges of the
neighboring cells in portions of transmit power zone `TPZ.sub.4.2`
1632 in AP `4` 1126 and in portions of `TPZ.sub.2.3` 1622 in AP `2`
1614. As likewise shown in FIG. 17, mobile station (MS) 1756 is
operating within `ICIZ.sub.2-4` 1638'and MS i' 1754 is operating
within `TPZ.sub.4.2` 1632, which contributes to the `ICIZ.sub.2-4`
1638. However, MS i' 1754 is not operating within `ICIZ.sub.2-4`
1638 itself
[0148] In an embodiment previously described in greater detail
herein, an AP broadcasts a set of power reference signals (PRS) for
each cell and uses the received power reference signal strength
(RPRSS) reported by a MS to determine its corresponding path loss
and transmit power zone (TPZ). In this embodiment, the AP
broadcasts the transmit power level associated with the PRS such
that the MSs can directly calculate and report the downlink path
loss. Assuming that the path loss is reciprocal, the MS may use
this calculation to determine if its uplink transmission will
interfere with receptions by a neighboring AP.
[0149] Referring now to FIG. 17, MS 1756 receives the PRS and the
associated transmit power level, TP .sub.4..sub.2 1638, from the
neighboring AP, AP `4` 1626. Based on the RPRSS, MS 1756 can
calculate the downlink path loss from AP `4` 1626, pathloss
(n.sub.U4), and estimate the uplink path loss to AP `4`, pathloss
(n.sub.U4) 1762, where:
pathloss (n.sub.U4).apprxeq.pathloss
(n.sub.D4)=(TP.sub.4.2-RPRSS.sub.nD4)
[0150] Likewise, AP `2` 1614 sends a mobile station resource map
(MRM) to MS 1756, which is used either independently or jointly
with AP `2` 1614 to determine the transmit power `TP.sub.nU2` 1760
to be used by MS 1756 for uplink transmissions to AP `2` 1614
during an upcoming transmission opportunity. In this embodiment, MS
1756 can estimate the strength of these uplink transmissions when
they are received by AP `4` 162 where:
RSS.sub.Un=TP.sub.nU2-pathloss (n.sub.U4)
[0151] If this estimated value is below some predefined threshold
(i.e. RSS.sub.Un<RSS.sub.thresh) 1, then any uplink resources
claimed by AP `4` 1626 in TPZ.sub.4.2 1632 may be deemed acceptable
in the resource contention report (RCR) sent by MS `n` 1756 to AP
`2` 1614, allowing AP `2` 1614 and AP `4` 1626 to schedule the
concurrent use of those uplink radio resources.
[0152] FIG. 18 is a is a simplified topological diagram showing an
embodiment of the disclosure for mitigating interference in a
contention-based system such as that of an IEEE 802.11 wireless
LAN. In this embodiment, a transmit power zone (TPZ) is defined by
the extent of a Request-To-Send (RTS) transmitted by an Access
Point (AP) at a certain transmit power level to a Mobile Station
(MS). As shown in FIG. 20, AP `1` 1804 comprises `TPZ.sub.1.1 1808,
`TPZ.sub.1.2` 1810, and `TPZ.sub.1.3` 1812, which respectively
correspond to `RTS(a)` 1850, `RTS(b)` 1852, and `RTS(c) 1854.
Likewise, AP `2` 1814 comprises `TPZ.sub.2.1` 1818, `TPZ.sub.2.2`
1820, and `TPZ.sub.2.3` 1822, with `TPZ.sub.2.2` 1820, and
`TPZ.sub.2.3` 1822 respectively corresponding to `RTS(d)` 1856 and
`RTS(k)` 1858. As likewise shown in FIG. 18, AP `4` 1824 comprises
`TPZ.sub.4.1` 1830 and `TPZ.sub.4.2` 1832, which respectively
correspond to `RTS(i)` 1862 and `RTS(h)` 1860.
[0153] As shown in FIG. 18, the inter-cell interference zone (ICIZ)
`ICIZ.sub.1-2A` 1836 between AP `1` 1804 and AP `2` 1814 occurs
mostly at the edges of `TPZ.sub.1.3` 1812 in AP `1` 1804 and of
`TPZ.sub.2.3` 1822 in AP `2` 1814. Likewise, `ICIZ.sub.2-4` 1838
between AP `4` 1824 and AP `2` 1814 occurs mostly at the edges of
`TPZ.sub.42` 1832 in AP `4` 1824 and `TPZ.sub.2.3` 1822 in AP `2`
1814. Likewise, the `ICIZ.sub.1-4` 1834 between AP `4` 1834 and AP
`1` 1804 likewise occurs mostly at the edges of `TPZ.sub.4.2` 1832
in AP `4` 1824 and `TPZ.sub.1.3` 1812 in AP `2` 1804.
[0154] In this embodiment, an inter-cell interference zone (ICIZ)
is a region where overlapping Requests-to-Send (RTS) are received
from different APs. For example, `ICIZ.sub.2-4` 1838 is the result
of an RTS transmitted from AP `2` 1814 to MS `k` 1858 at the same
time that an RTS is transmitted from AP `4` 1824 to MS `g` 1852.
Accordingly, the RTS acts as both a claimed zone resource map
(CZRM) and as a mobile station resource map (MRM). The source
address in the RTS frame identifies the AP claiming the resources
and the destination address in the RTS frame identifies the MS
being assigned the resources. For example, when the RTS transmitted
from AP `2` 1814 is received by MS `k` 1858 and MS `g` 1852, this
is an indication to both MSs that the radio resources have been
claimed by AP `2` 1814 and assigned to MS `k` 1858.
[0155] Likewise, the Clear-To-Send (CTS) transmitted by a MS acts
as a resource contention report (RCR) both to the serving AP and to
neighboring APs. It is equivalent to notifying the serving AP that
the resource assignment is acceptable and to notifying the
neighboring APs that they should not use these resources. For
example, when the CTS(k) 1864 transmitted from MS `k` 1864 is
received by AP `2` 1814 and AP `4` 1824, it serves as an indication
to AP `2` 1814, the serving AP, that the resource assignment was
successful and serves as an indication to AP `4` 1824, the
neighboring AP, that its claim in the RTS sent to MS `g` 1852 was
not successful and that it should refrain from using the radio
resources for the period defined by the CTS.
[0156] From the foregoing, it will be apparent to skilled
practitioners of the art that the use of mobile station-assisted
interference mitigation procedures in a heterogeneous wireless
network environment enables dynamic radio resource allocation
across neighboring cells. Furthermore, such resource allocation
accommodates both cell edge and overlay interference scenarios and
likewise provides management of radio resources in the time,
frequency and spatial (i.e., transmit power) domains and may be
extended to the coding dimension.
[0157] Moreover, the allocation of radio resources can be based on
instantaneous demand rather than statistical averaging of traffic.
Likewise, the determination of coverage and interference zones can
be based on information and measurement of signals actually
received from serving and neighboring cells, which reflect true
conditions in the propagation environment. Furthermore, real-time
coordination can be achieved between APs that may not be able to
communicate directly (e.g. via a backhaul network). Likewise,
direct communication is only required between a MS and its serving
AP as the MS only needs to monitor broadcasts from interfering
neighbor APs. Furthermore, the degree of interference allowed
between cells can be dynamically adjusted by changing transmit
power levels based on resource conflict and usage reports received
from the same MSs that are the target of an upcoming transmission.
Likewise, radio resource coordination is enabled with macro (e.g.,
eNB) cells in femtocell (e.g., HeNB) deployments.
[0158] Those of skill in the art will likewise recognize that
prevalent approaches within the wireless industry do not currently
use feedback from the MS as a mechanism for dynamically managing
the use of radio resources across a network. More specifically, the
current approaches listed below embody the following
limitations:
[0159] Multi-channel spectrum planning. The available spectrum is
sub-divided into a number of non-overlapping channels and each cell
within an AP is configured with the identity of the channel that it
is to use. Off-line planning is used to ensure that cells within a
neighboring AP are assigned different channels so that they do not
interfere with each other. Accordingly, lower system capacity
results due to the static partitioning of the available spectrum.
In addition, off-line planning can be manually intensive and
require network monitoring.
[0160] Dynamic frequency allocation. As before, the available
spectrum is sub-divided into a number of non-overlapping channels.
However, each Access Point dynamically determines which channel(s)
it should use based on an algorithm. While this solution eliminates
some of the manual labor associated with multi-channel spectrum
planning, it still results in lower system capacity due to the
static partitioning of the available spectrum.
[0161] Fractional frequency reuse (FFR). The available spectrum is
sub-divided into a number of non-overlapping sub-bands and each
cell within an AP is configured with the identity of the sub-band
that it is to use in the edge region of its cell. In central
regions of the cell closer to the AP, it can attempt to use all of
the radio resources within the available spectrum. Off-line
planning is used to determine the transmit power level to be used
by an AP that marks the boundary between an edge region and a
central region. This approach results in lower system capacity due
to the static partitioning of the available spectrum in the edge
region of the cell. In addition, off-line planning can be manually
intensive and require network monitoring.
[0162] Adaptive fractional frequency reuse (AFFR). An AP may be
configured with one or more FFR profiles where each profile defines
the sub-band to be used in the edge region and the transmit power
level determining the boundary between an edge region and a central
region. The AP adjusts its operation to migrate between profiles
based on the level of interference reported by its MS or based on
signaling received from neighboring APs via the backhaul network.
The adjustments in sub-band allocation and transmit power levels
happen infrequently and must be coordinated by signaling over the
backhaul network to prevent "flapping" between profiles as the
neighboring APs also attempt to adjust to different profiles.
[0163] In contrast, the embodiments of the disclosure previously
described in greater detail herein provide the following
capabilities: [0164] Interference mitigation exploits multiple
dimensions of the radio resource domain--time, frequency and space.
Existing solutions only focus on the frequency dimension. [0165]
Mobile Stations act as a conduit for passing information between
APs, allowing information to be exchanged in real-time between
them, that in other circumstances, they would not be able to
communicate. Existing approaches rely on the existence of a common
backhaul network to allow communications between APs. Accordingly,
cooperation between APs is not possible if this common network does
not exist (e.g. if the APs are in different administrative domains
or in different radio access networks). [0166] The detection of
inter-cell interference zones is based on reception of over-the-air
(OTA) signals by a MS from neighboring cells which, by its very
nature, reflects the actual--and dynamically changing--propagation
environment in which each individual MS operates. Existing
approaches rely on modeling techniques that are less accurate and
do not cater to the conditions currently being experienced by an
individual MS. [0167] The dynamic detection of inter-cell
interference zones accommodates deployment scenarios that involve
overlapping coverage at the edges of a cell, underlay coverage
provided by micro-, pico- and femto-cells, and irregular islands of
coverage resulting from the vagaries of the RF propagation
environment. Existing approaches only deal with overlapping
coverage at the nominal (e.g., circular) edges of a cell. [0168]
The detection and avoidance of resource conflicts is dynamic and
does not rely on off-line planning. Existing approaches are static
and are based on off-line measurements and spectrum planning.
[0169] The detection of resource conflicts, and the selection of
available resources, is based on the actual assignment of radio
resources by APs that is updated in real-time with their
anticipated usage. Existing approaches rely on statistical
averaging of resource usage to statically partition resources
amongst potentially contending APs. [0170] Radio resources are
dynamically claimed and allotted to APs based on their
instantaneous traffic requirements; these assignments can then be
adjusted based on real-time feedback of resource conflicts.
Existing approaches statically partition radio resources amongst
APs, based on their potential for experiencing resource
contention.
[0171] Although the described exemplary embodiments disclosed
herein are described with reference to mitigating interference
between access points in a heterogeneous wireless network
environment, the present disclosure is not necessarily limited to
the example embodiments which illustrate inventive aspects of the
present disclosure that are applicable to a wide variety of
authentication algorithms. Thus, the particular embodiments
disclosed above are illustrative only and should not be taken as
limitations upon the present disclosure, as the disclosure may be
modified and practiced in different but equivalent manners apparent
to those skilled in the art having the benefit of the teachings
herein. Accordingly, the foregoing description is not intended to
limit the disclosure to the particular form set forth, but on the
contrary, is intended to cover such alternatives, modifications and
equivalents as may be included within the spirit and scope of the
disclosure as defined by the appended claims so that those skilled
in the art should understand that they can make various changes,
substitutions and alterations without departing from the spirit and
scope of the disclosure in its broadest form.
* * * * *